1. Field of the Invention
The invention relates to a method and device for washing and aspirating coated objects used in diagnostic assays. More particularly the invention is used to wash coated objects in the receptacles in which the diagnostic assay is performed. By way of further characterization, the invention includes a washing device which seals the receptacle into which it is inserted while injecting and aspirating cleaning fluid in a manner that produces movement of the coated object to permit complete cleaning thereof.
2. Description of the Related Art
In the diagnostic assay for the presence of hepatitis virus in blood, plastic beads coated with antibody are located in a tube-like receptacle or well. Patient serum is added to the receptacle. During incubation, antibody in the serum binds to the antibody. The serum is then removed from the receptacle and the bead is washed and aspirated with a cleaning fluid. Next, a reagent containing an antibody tagged with iodine-125 is added and binds to any antigen on the bead to form an antibody-antigen-antibody sandwich. The reagent is removed from the receptacle and the coated bead is again washed and aspirated with a cleaning fluid to ready the receptacle and coated bead for further processing in a gamma counter.
In the processing of the beads it is very important that the washing of the beads be complete to remove all serum and reagent and all unbound antigen and antibody. Further, it is extremely important that the washing step be accomplished without leakage or uncontrolled escape of the virus containing serum.
Previously, the washing of serum from beads was accomplished by repeated rinsing of the beads. That is, the washing fluid was poured over the bead and then rinsed from the receptacle containing the bead. When using this method it is difficult to remove all of the washing fluid such that a small amount of contaminated serum remains after each washing step. Therefore, although diluted by each subsequent washing, a small amount of the contaminated serum may remain even after repeated washings. Because removal of all the contaminated serum is important, this washing procedure has been less than satisfactory. An additional problem resulting from this procedure is that possible contamination due to spillage, splashing, or aerosolization of the washing substance may occur. This may present a danger to testing personnel and may contaminate associated apparatus.
In order to speed up the washing process, mechanical washing devices have been used. Devices presently marketed by Abbott Laboratories Inc. under the trademarks of UNIWASH and PENTAWASH and described in U.S. Pat. No. 3,949,771 use a wash probe which is lowered into the reaction tray well until the probe tip touches the bead and the tip is as far as possible into the well. An integral spray device is activated such that the washing substance is sprayed onto the sides of the well. A vacuum tube is positioned on the probe above the bead contact point such that the bead is retained against the device by the vacuum. While suited for its intended purpose, the device does not draw the washing substance over the entire surface of the bead. That is, the contacted areas of the bead are not sufficiently washed to remove all of the contaminated serum. The proximity of the bead to the well hinders the circulation of the washing substance around the bottom of the bead. In addition, no provision is made for preventing contaminated washing substance from escaping the well as by splashing and spillage.
Another device, illustrated in U.S. Pat. No. 4,053,284 issued to N. A. Posch on Oct. 11, 1977, seals the well to prevent escape of contaminated serum from the well. This device uses a probe which is inserted into the well and which employs a stopper like device around its upper portion. The device is inserted into the well such that the washing portion extends into the well and the stopper seals the well from the outside atmosphere. The beads to be washed are contained in a reaction area at the bottom of the well. The reaction area is screened from the rest of the well such that the beads are prevented from moving to other parts of the well. The centermost portion at the bottom of the well is vacant such that the vacuum tube attached to the wash probe may extend near the bottom of the well. The washing fluid is drawn into the well by the vacuum through ports in the washing probe. The washing fluid then flows down the side of the well and over the beads. The fluid collects at the center of the well and is drawn up through the vacuum tube. While suited for its intended purpose, the beads are confined in the cleaning area by the screens and touch both each other and the walls of the well. As such, the entire surface of the beads may not be washed thereby allowing some contaminated hepatitis serum to remain on the beads. A single larger bead may be washed with this device in the same manner as the smaller beads. That is, the single large bead is washed by the same method except that no screening is necessary to keep the bead from being drawn up through the vacuum tube. Instead, the bead is positioned between the vacuum tube and the wall of the well. The bead thus contacts both the well and the side of the vacuum tube thereby hindering the circulation of the washing fluid and resulting in incomplete washing of the contacting surfaces.
It would be desirable to have an irrigating device in which the object may be moved by or suspended in the cleaning fluid in order that all surfaces of the object may be contacted by the fluid.